Planar fuel cell based electrical power generators contain a gas permeable membrane which allows atmospheric gases access to a hydrogen generating fuel in a fuel cartridge, prior to insertion of the cartridge into the power generator.
During operation, water vapor generated by the fuel cells diffuses through the gas permeable membrane and reacts with the fuel to generate hydrogen. The hydrogen diffuses in the opposite direction back to the fuel cell where it is used to generate electricity and additional water vapor.
This configuration requires that a large surface area gas seal be formed around the perimeter of the cartridge, which is difficult to achieve in practice. Further, there is no way to completely eliminate the atmospheric gases that are admitted into the system when the cartridges are being replaced, creating a potentially dangerous mixture of hydrogen and oxygen.